Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. The composition of sand is highly variable, depending on the local rock sources and conditions. In nature, sand also varies in particle size. Depending on the source, the sand particle size range can vary, e.g. particle diameters as small as 0.02 mm were considered sand under the Albert Atterberg standard in use during the early 20th century. Under the American Association of State Highway and Transportation Officials, the minimum sand diameter size is 0.074 mm, while the United States Department of Agriculture is at 0.05 mm. Sand may be further classified according to grades. ISO 14688 grades sands as fine, medium and coarse with ranges 0.063 mm to 0.2 mm to 0.63 mm to 2.0 mm. In the United States, sand is commonly divided into five sub-categories based on size: very fine sand ( 1/16−⅛ mm diameter), fine sand (⅛ mm−¼ mm), medium sand (¼ mm−½ mm), coarse sand (½ mm−1 mm), and very coarse sand (1 mm−2 mm).
Sand has been the component of many different applications such as in agriculture; recreational aquariums; geo-textile; beach nourishment; brick, cob, concrete, glass, and mortar manufacturing; landscaping; paint texture; railroad traction; sand casting; sandbags; sandblasting; water filtration; and fracking. However, in many industrial applications, before sand can be efficiently utilized, its chemical and/or physical properties must be modified or altered for the intended purpose. For example, sand has been widely used in fracking.
In order to improve fracking, it is highly desirable to employ sand with certain fracking properties. For example, among other properties, the sand used should have the mechanical strength to withstand closure stresses to hold fractures open after the fracturing pressure is withdrawn. Large mesh sands have greater permeability than small mesh sands at low closure stresses, but will mechanically fail (i.e. get crushed) and produce very fine particulates (“fines”) at high closure stresses such that smaller-mesh sands overtake large-mesh sands in permeability after a certain threshold stress. Untreated sand is prone to significant fines generation; fines generation is often measured in wt % of initial feed.
Another property desirable for fracking relates to the geometry of the sand. I Certain shapes or forms amplify stress on the sand particles, thus decreasing its strength and making them especially vulnerable to crushing. Thus, sand used in fracking should have ideal sphericity and roundness properties. In addition to the shape of the individual sand particle, it is also desirable to employ sand characteristic of certain cluster and turbidity values.
Though there are known methods in the art to modify sand into sand with fracking properties; these methods often require multiple steps that results in increased cost and time to produce. In addition, the general methods known to modify sand into sand with fracking properties often require the use of non-contaminated sand. Thus, there is a need for a cost and/or time effective method to modify sand into sand with fracking properties. There is also a need for a method that can decontaminate sand, thereby allowing the re-usability of the sand.